Clock Domain Crossing MTBF Calculator

Synchronizer Configuration

FPGA Family Preset

Source Clock Frequency (F_SRC)

MHz

Destination Clock Frequency (F_DST)

MHz

Synchronizer Stages

Number of Synchronizers in Design

Total number of CDC synchronizers in the design (MTBF is divided by this count)

Xilinx 7-Series: τ = 45 ps · T_w = 20 fs · T_setup = 50 ps

Mean Time Between Failures

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T_slack Available

—

Metastability Events / Second

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Stages	T_slack (ns)	MTBF	Verdict	Recommended?
Click Calculate to compare stages

Understanding Clock Domain Crossing Metastability

When a signal crosses between two asynchronous clock domains, the destination flip-flop may sample the signal during its transition — violating setup/hold times. This puts the flip-flop into a metastable state where the output is neither 0 nor 1 for a brief period.

The MTBF Formula

The probability of metastability propagating through a synchronizer chain is:

MTBF = e^{(T_slack / τ)} / (F_src × F_dst × T_w × N_syncs)

T_slack = (N_stages - 1) × T_{clk_dst} - T_setup — time available for metastability to resolve
τ — Resolution time constant of the flip-flop (technology dependent)
T_w — Metastability window width (vulnerability window)
N_syncs — Total number of independent synchronizers in the design

Design Targets

> 100 years — Safe for commercial designs
> 1,000 years — Recommended for industrial applications
> 1,000,000 years — Required for safety-critical (aerospace, medical)

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Synchronizer Configuration

Stage Count Comparison

Understanding Clock Domain Crossing Metastability

The MTBF Formula

Design Targets